The django.contrib.gis.measure module contains objects that allow
for convenient representation of distance and area units of measure. [1]
Specifically, it implements two objects, Distance and
Area – both of which may be accessed via the
D and A convenience aliases, respectively.

Distance objects may be instantiated using a keyword argument indicating the
context of the units. In the example below, two different distance objects are
instantiated in units of kilometers (km) and miles (mi):

Area attributes are the same as Distance attributes,
except they are prefixed with sq_ (area units are square in nature).
For example, Area(sq_m=2) creates an Area object
representing two square meters.